netdev - Re: [PATCH net-next 09/14] tg3: Improve small packet performance

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Message-ID: <20100804230825.GQ29316@kryten>
Date:	Thu, 5 Aug 2010 09:08:25 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	Michael Chan <mchan@...adcom.com>
Cc:	Matthew Carlson <mcarlson@...adcom.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"andy@...yhouse.net" <andy@...yhouse.net>
Subject: Re: [PATCH net-next 09/14] tg3: Improve small packet performance

 
Hi,

> We generally only get an estimate of the available tx ring size when we
> call tg3_tx_avail(), so memory barriers are not generally needed.  We
> put a compiler barrier there to make sure that the compiler will fetch
> the tx_prod and tx_cons from memory to give us a better estimate.
> 
> In specific cases detailed in the patch description, we do need memory
> barriers when we call netif_tx_stop_queue() and then check for the tx
> ring.  We decided to put memory barriers exactly where they're needed
> instead of inside tg3_tx_avail() which is an overkill.

Thanks Matt and Michael. I was pretty sure you were thinking about
ordering issues but wanted to double check.

Anton
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